The subject matter disclosed herein relates to gas turbines and, more particularly, to an adjustable mount for an air impingement cooling manifold for a gas turbine.
Air impingement cooling is used to manage the casing temperature of a gas turbine and to reduce and maintain the clearances between rotating blades and accompanying interior casing surfaces. The cooling of the casing in general needs to be relatively uniform to avoid undesired non-roundness and local stress concentration. The efficiency of cooling is affected by various air impingement cooling configurations. One problem with air impingement cooling configurations on gas turbines is the difficulty in achieving a relatively uniform heat transfer coefficient across large, non-uniform, non-standard casing surfaces. On some gas turbines, small impingement holes and relatively short nozzle to surface distances are applied. While these features may produce the required higher heat transfer coefficients on the casing, a problem with the use of relatively small impingement cooling holes is the need for operating with a relatively high differential pressure drop across the holes. This results in the requirement for undesirable high cooling air supply pressures which negatively impacts net efficiency for gas turbines. Also, relatively smaller holes and shorter hole to surface distances have detrimental cross flow and an inadvertent effect on cooling efficiency of constant coolant flow rate. Consequently, a high pressure blower may be needed with added system capital and operational cost.
One known air impingement cooling configuration includes a plurality of manifolds affixed to the turbine casing directly above the target cooling area. The manifolds are typically affixed to the turbine casing using mounts. Cooling air is provided to the manifolds, which have a series of air impingement holes formed in a lower plate of each manifold. The size and positioning of the impingement holes on the lower plates are selected to produce a relatively uniform and desired heat transfer coefficient across the turbine casing targeted for cooling by the air impingement cooling system. With this type of manifold cooling system, the distance between the lower plate of each manifold and the turbine casing determines the cooling of the casing achieved by the manifolds. However, the mounts that affix the manifolds to the casing are problematic in that they do not allow for any adjustment of the gap distance between the lower plate of the manifold and the turbine casing while the manifold is mounted to the casing. The mount gap distance can only be adjusted with the manifolds removed from the casing. This results in an undesirable, time consuming trial and error method needed to achieve the desired gap distance between the lower plate and the casing. That is, typically the manifolds need to be placed on and off the casing several times until the desired gap distance and, thus, the proper amount of cooling of the casing is achieved.